Transcript EVOLUTION

EVOLUTION
Variation
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The differences between individual members
of a population (ex: fur color, eye color, etc.)
Can not always be observed
Are almost always genetically inherited
Results from mutations and recombination
Adaptation
An inherited trait
that increases the
population’s
chances of
survival and
reproduction
 It can be physical
or behavioral
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Evolution
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Defined as “change over time”
There were 3 scientists who made important
contributions to this field:
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Charles Bonnet
Jean-Baptiste Lamarck
Charles Darwin
Charles Bonnet
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Noticed that fossils didn’t look like modern
organisms
Theorized that periodic catastrophes affected
the entire planet and after each catastrophe
life began anew
Jean-Baptiste Lamarck
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Challenged Bonnet’s views
Believed that the fossils of extinct animals
were the ancestors of those living today
Developed Lamarck’s hypothesis
Lamarck’s Hypothesis
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Organisms strive to improve themselves
Principle of Use and Disuse: the mostused body structures develop, whereas
unused structures waste away
Principle of Inheritance of Acquired
Characteristics: modified structure is
inherited by the organism’s offspring**
**This 3rd principle was disproved by August Weismann. Changes in an
individual during its lifetime do not affect its reproductive cells or its
offspring.
Charles Darwin
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Scientist who studied plants and animals
while on an around-the-world trip
After studying several organisms, he
developed his theory of evolution—Natural
Selection
Natural Selection
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There is variation within populations
Some variations are favorable [favorable
variations improve an organism’s ability to
function and reproduce in its own particular
environment]
Not all young produced in each generation
can survive
Individuals that survive and reproduce are
those with favorable variations
Rate of Evolution
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Gradualism:
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states that evolution occurs at a slow, gradual rate
this is what Darwin believed
Punctuated Equilibrium:
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states that populations remain genetically stable
for long periods of time, interrupted by brief
periods of rapid genetic change
this new theory was first stated by Stephen Jay
Gould and Niles Eldridge
Comparing Anatomy
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Homologous Structures:
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structure or characteristic with similar functions
found in different species
thought to be inherited from common ancestors
EX: humans, whales, and bats all have the same
number and type of bones in the forelimbs
Comparing Anatomy (cont.)
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Analogous Structures:
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structures that are similar in function, but are
not inherited from a common ancestor
EX: wings of insects and wings of birds
Comparing Anatomy (cont.)
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Vestigial Structures:
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structures that are inherited,
but reduced in size and often
unused
suggest structures of the
ancestors of modern
organisms
EX: pythons have vestigial hip
and leg bones
Types of Evolution
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There are 5 different types of evolution:
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Speciation
Divergent Evolution
Convergent Evolution
Coevolution
Adaptive Radiation
Speciation
new species
species
original species
Divergent Evolution
new species
species
new species
Convergent Evolution
species
new species
new species
species
These 2 new species share many traits.
These two succulent plant
genera, Euphorbia
and Astrophytum, are only
distantly related, but have
independently converged
on a very similar body form.
Coevolution
species
species
original species
with new traits
original species
with new traits
Bumblebees and the
flowers they pollinate
have coevolved so
that both have
become dependent
on each other for
survival
Adaptive Radiation
species
new species
new species
new species
new species
new species
Population Genetics
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Populations are the smallest unit in which
evolution takes place
Population genetics is the study of genetic
traits and changes in populations
Hardy-Weinberg Principle
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If a population is not evolving, the allele
frequencies in the population remain stable
The population is said to be in genetic
equilibrium
Conditions Required to Maintain
Equilibrium
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No natural selection
Random mating
No migration
No mutation
Very large population size
Types of Selection
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In stabilizing selection,
the extreme phenotypes
are selected against
Types of Selection (cont.)
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In directional selection, there is a shift in
frequency to an extreme phenotype
Types of Selection (cont.)
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In disruptive selection, the most common variation
in a population is not favored